Machine tool with an optical measuring device for three dimensional registration between the tool holder and the work holder

ABSTRACT

A machine-tool including a machining module equipped with a tool-holder and a work-holder, and an optical measuring device-for the three-dimensional measurement of the relative position between the tool-holder and the work-holder. The optical measuring device includes an optical system mounted on the work-holder and a target mounted on the tool-holder. The target includes a useful face forming a positioning reference that can be placed in the optical axis of the optical system.

TECHNICAL FIELD

The present invention relates to the field of machine-tools. The presentinvention relates also to the field of the optical measurement of therelative position between a first object and a second object, and inparticular between the tool-holder and the work-holder of amachine-tool.

In the machine-tool field, carrying out inter alia machining by materialremoval, there is a need to accurately know the relative positionbetween the tool-holder and the work-holder, in order to ensure amachining range conforming to the machining plan developed duringadjustment.

The production of workpieces by means of machining modules(machine-tools), in particular auto lathes, automatic turning machines,turning-milling centres, milling machines, machining centres andtransfer machines, typically comprises three distinct phases.

In a first adjustment (or presetting) phase, the operator (for examplean auto lathe operator) defines and tests, on a machining module, themachining plan, that is to say the succession of operations and of axisdisplacements necessary to obtain the desired workpiece to be machined.The operator is for example careful to obtain the most effectivepossible machining plan, that is to say the one which makes it possibleto machine a given workpiece with a minimum of operations and avoidingcollisions between tools or with the workpiece. He or she chooses thetools to be employed, and checks the quality of the workpieces obtained,for example the surface conditions, compliance with tolerances, etc.

In a second production phase, a series of workpieces are produced on thepreset machining module, with the parameters defined during adjustment.This phase is the only productive phase; it is often performed 24 hoursa day, the machining module being supplied with raw material by means ofan automatic magazine feed or a loader of slugs (raw workpieces).

It may be that the production of a series of workpieces is interrupted,for example to replace the worn tools, to produce another type ofworkpiece on the same machining module, for machine maintenance etc.,then subsequently restarted. In such a case, a makeready phase isnecessary to apply the parameters defined previously during adjustment.This makeready phase is faster than adjustment.

During makeready, it is often necessary to replace the tools mounted onthe machine with another set of tools suitable for the machining whichis to be performed. The accuracy of the positioning of these toolsdetermines the quality of the machining, but it is difficult toreproduce in successive makeready phases.

In addition, during the production phase it is not impossible to have,as the machining of new workpieces progresses, and in particular forlong runs, drifts of position between the tool-holder and thework-holder, drifts which are due in particular to the thermal expansionof the machines.

STATE OF THE ART

Various solutions have therefore been proposed in the prior art in orderto guarantee a correct relative positioning between the tool-holder andthe work-holder during the production phase and during makeready, thatis to say a relative positioning that conforms to the relative positionbetween the tool-holder and the work-holder during adjustment.

Many in-situ measurement techniques used in machine-tools aim to measurethe relative position between the workpiece or the work-holder and thetool itself. However, in this case, the measurement of the relativeposition between the workpiece or the work-holder and the tool isaffected by the effects of the wear of the tool and of the thermal driftof the machine-tool during its operation.

Also, this type of relative position measurement is generally performedin two dimensions, that is to say in two directions, as in the documentDE202016004237U.

Since this relative registration between the workpiece or thework-holder and the tool is limited to two dimensions (for example Y andX, respectively the lateral and vertical directions), it is notsufficiently comprehensive to ensure the correct relative position, suchthat another technique has to be used to measure the third dimension(for example Z, the direction of advance/of retraction of thework-holder, also called “material direction”). This situation increasesnot only the cost of the measurement technique, but also theimplementation time thereof, and it also adds an error through the useof two series of measurement simultaneously.

The document US2014362387 AA discloses an optical measuring deviceplaced on the tool-holder and that makes it possible to check that atarget object does not interfere with the tool-holder. This opticalmeasuring device uses a gauging element with several inclined parts tocharacterize the geometric parameters of the laser ray measuring device,in particular the position between the sensor of the reflected ray andthe emitter of the incident ray. This gauging element is not involved inmeasuring the relative position between the tool-holder and the targetobject which can be a workpiece to be machined.

The document US2010111630 AA discloses a tool repositioning system for amachine-tool, comprising targets of irregular form situated on the tooland that allows for the optical measurement of the precise position ofthe tool by optical measuring elements whose position is not specified.

The document U.S. Pat. No. 5,831,734 describes a solution in which anoptical sensor is secured to the tool-holder and performs theregistration of the relative position of this tool-holder relative to aworkpiece to be machined provided with a distinctive mark (groove).

The document JP07246547 proposes a machine-tool which is equipped with areflector installed on a tool mounting shaft, and a measuring devicewith several laser interferometers capable of registering the positionof the reflector.

These solutions do not however make it possible to be able to determine,by a single exposure step, the relative position between the workpieceto be machined and the tool, this single exposure step giving theinformation that makes it possible to determine this relative positionin the three dimensions of space.

Nor do these solutions make it possible to become independent of theparameters that are variable in real time during the machining, inparticular the wear of the tool and the thermal variations of the tooland/or of the work space of the machine-tool which receives theworkpiece to be machined.

BRIEF SUMMARY OF THE INVENTION

One aim of the present invention is to propose a technology that makesit possible to perform a measurement of relative position between atool-holder and a work-holder, that is free of the limitations of theknown measurement techniques.

Another aim of the invention is to propose a technology that makes itpossible to perform a measurement of relative position between atool-holder and a work-holder, which provides the three-dimensionalrelative position between the first object and the second object from asingle exposure step.

According to the invention, these aims are achieved in particular bymeans of a machine-tool comprising a machining module equipped with atool-holder and a work-holder, and an optical measuring device for thethree-dimensional measurement of the relative position between saidtool-holder and said work-holder, said optical measuring devicecomprising an optical system with an image acquisition system, mountedon the work-holder and a target mounted on the tool-holder andcomprising a useful face forming a positioning reference that can beplaced in the optical axis of the optical system.

According to the invention, the optical measuring device is configuredto make it possible, through a single step of exposure of the target bythe optical system, to determine the three-dimensional relative positionbetween the holder of the workpiece to be machined and the tool-holder.In this way, it is possible to obtain, through the exposure of thetarget performed by the optical system, the exact position between saidtool-holder and said work-holder. This exposure corresponds to thetaking of image(s) of the target by the optical system, namely theacquisition, the capturing or the recording of one or more images of thetarget. In particular, according to one possibility, the optical systemis capable of simultaneously taking a first image and a second image ofthe target. These two images (pair of images) contain information on therelative position between the target and the optical system, whichinformation makes it possible to obtain the relative position in thethree directions of space (in particular on X, Y and Z) between thetarget and the optical system. According to a variant, the opticalsystem is capable of taking a succession of pairs of images of thetarget.

In particular, the target is positioned such that the image focal planeof the optical system can be merged with the useful face of the target.

According to one embodiment, the target is a three-dimensional targetcomprising, on a useful face:

-   -   a first structure defining a planar reference face, and    -   a second structure having a face that is inclined relative to        said planar reference face, and said optical system comprises a        first exposure system and a second exposure system, in which the        difference between the focal distance of the second exposure        system and the focal distance of the first exposure system lies        between the minimum distance and the maximum distance separating        the reference face from the inclined face.

Thus, the optical system can simultaneously identify its positionrelative, on the one hand, to the reference face (or first referenceface) via the image generated by the first exposure system and, on theother hand, to at least one zone of the inclined face (or secondreference face) which is identified via the image generated by the firstexposure system, and whose location on the target is known relative tothe reference face.

This target also possibly conforms to one or other or several of thefollowing provisions:

-   -   the planar reference face is divided up between at least a first        portion whose surface is reflective according to first        reflection parameters, and a second portion whose surface is        reflective according to second reflection parameters different        from the first reflection parameters;    -   the surface of said first portion is reflective according to a        diffuse reflection, and the surface of said second portion is        reflective according to a specular reflection;    -   said second portion is divided up according to a series of        localized zones positioned in the first portion;    -   the surface of said inclined face has relief elements or else        specular elements that are evenly distributed;    -   the localized zones define between them a geometrical figure        belonging to the following list: quadrilateral, parallelogram,        rectangle, square, rhombus, regular polygon and circle;    -   the localized zones of said second portion are formed by islands        or segments distributed in the first portion;    -   the localized zones are made of chromium;    -   the first structure and the second structure are positioned on        the useful face concentrically to one another, in particular the        first structure surrounds the second structure;    -   the localized zones of the second portion of the first structure        define a square which surrounds the second structure;    -   the first structure delimits an aperture for a housing housing        said second structure;    -   the second structure is positioned in said housing with the        inclined face which is set back relative to the reference face        of said first structure, in particular at the back, behind the        plane delimited by the reference face;    -   the surface of the inclined face of the second structure is        striated, in particular the surface of the inclined face of the        second structure is covered by one of the following elements:        etched network, structured grid or network of specular lines.

According to one embodiment, the surface of this inclined face hasevenly distributed relief elements. According to another embodiment, thesurface of this inclined face has evenly distributed specular elements.In both cases, the idea is to be able to register the inclined face,which is roughly planar, in a direction Z orthogonal to the referenceface. To do this, in one case, the relief elements constitute surfaceirregularities or roughnesses of small size, the surface of the inclinedface being rough and making it possible to form a diffuse reflectionwhich allows an optical system which looks at the target to clearly seea portion of the inclined face: in particular, these relief elementshave a size greater than 700 nanometres, in particular greater than 1micrometre, namely of a size greater than the wavelength of the incidentradiation, here natural light. In the other case, the specular elementsof the inclined face, positioned according to a geometrical arrangement,for example in mutually parallel lines and positioned at differentpositions according to the direction Z, are visually distinguished fromthe rest of the surface of the inclined face (which is preferablyreflective according to a diffuse reflection), hence the possibility foran optical system which looks at the target to clearly see a portion ofthe inclined face with one or more of these specular elements.

This three-dimensional target has, on its side forming the useful face,a dual structure, respectively defining a first planar reference faceand a second reference face, defining a plane that is inclined relativeto the first reference face. This three-dimensional geometry of thetarget, allied with specific and different optical characteristics ofthe surfaces that respectively make up the first reference face and thesecond reference face, allow for an optical registration in the threedimensions X, Y and Z of space of this target relative to the opticalsystem used. In one embodiment, this optical system makes it possible toperform this optical registration, namely culminating in the measurementof relative position, by virtue of a single step of exposure both of thefirst planar reference face and of the second inclined reference face:it therefore involves a simultaneous exposure of the image of the firstplanar reference face and of the second reference face. Thissimultaneous exposure can be done in two, three or more iterations, evenin bursts over n exposures (n being an integer greater than one, forexample ranging from two to fifteen). In this way, it is possible tohave several images (a series of images) both of the first planarreference face and of the second reference face, which makes it possibleto perform a processing by computation algorithms, not of a single imageof the first planar reference face and of the second reference face, buta processing of the series of images both of the first planar referenceface and of the second reference face, and thus gain in accuracy.

In particular, according to one possible provision, this generation ofimage(s) of the first planar reference face and of the second referenceface is performed by the optical system used without having to performan adjustment, as will be explained later. In this case, there is nospecific setting to be performed in the optical system, which allows fora significant time saving in the performance of the measurement of therelative position of the three-dimensional target. This solution notablyoffers the advantage over the prior art of not requiring either severalmeasurement steps or even the modification of the settings and inparticular the focal distance of the optical system which is looking atthis target.

Also, when this target is used for measurement of relative positionbetween a tool-holder and a work-holder, it is possible to becomeindependent of the wear of the tool and of the thermal variations of thetool and/or of the work space of the machine-tool which receives theworkpiece to be machined by placing this target on the tool-holder.

In one embodiment, the optical system comprises a first exposure systemand a second exposure system, in which:

-   -   the depth of field of the first exposure system is at least 10        times greater than the depth of field of the second exposure        system, and    -   the optical system is arranged such that the optical path of the        first exposure system and the optical path of the second        exposure system have a common section placed on the optical axis        of the optical system and comprising the image focal plane of        the first exposure system and the image focal plane of the        second exposure system.

Such an optical system can be placed on one of the two objects concerned(a second object formed by a work-holder) and allows, through the twoexposure systems, a simultaneous taking of two sharp images at twolocations adjacent to one another on the other of the two objects (afirst object formed by a tool-holder), these two locations of the firstobject being situated at a slightly different distance from the secondobject. Such an optical system makes it possible, as will be describedin detail hereinbelow, through the two images, to three-dimensionallyregister the relative position between the first object and the secondobject which bears the optical system.

In one embodiment, the optical system is arranged such that the opticalpath from the object (first object) passes through at least a portion ofone out of the first and the second exposure systems before reaching theother of the first and the second exposure systems. In this way, it ispossible to have a section of optical path as input/output of theoptical system which is common or very close for the first and thesecond exposure systems. It is thus possible not only to combine thefirst and the second exposure systems on the same optical system butalso to be able to register two locations that are adjacent to oneanother on the first object, which are close to a few tens ofmillimetres, even a few millimetres, even less than a millimetre.

In one embodiment, the first and the second exposure systems arepositioned in parallel to one another and the optical system alsocomprises an optical module positioned between the first and the secondexposure systems and configured to deflect some of the light rayspassing through at least a part of one out of the first and the secondexposure systems to the other out of the first and the second exposuresystems. According to one possibility, this optical module is orincludes a catoptric optical system such as a mirror:

This optical system also possibly conforms to one or other or several ofthe following provisions:

-   -   the focal distance of the second exposure system is greater than        the focal distance of the first exposure system,    -   the enlargement of the first exposure system is less than or        equal to the enlargement of the second exposure system,    -   the depth of field (DOF1) of the first exposure system is        greater than or equal to 0.8 millimetres,    -   the depth of field (DOF2) of the second exposure system is less        than or equal to 0.1 millimetres,    -   the first exposure system is telecentric and the second exposure        system is telecentric,    -   the first exposure system is configured such that its image        focal plane can correspond to the reference face of the first        structure, and    -   the second exposure system is configured such that its image        focal plane can be secant with the inclined face of the        three-dimensional target,    -   the optical device also comprises a third exposure system        positioned on the tool-holder and configured to register the        orientation of the useful face of the target and/or the angular        orientation of the tool-holder.

The present invention relates also to a method for three-dimensionaloptical measurement according to three orthogonal directions X, Y and Zin the three-dimensional space of a machine-tool, between a tool-holderand a work-holder that are aligned and remote from one another in themain direction Z, in which:

-   -   an optical system is provided with an image acquisition system,    -   said optical system is mounted on the work-holder,    -   a target is provided comprising a useful face forming a        positioning reference,    -   said target is mounted on the tool-holder,    -   the tool-holder and the work-holder are positioned such that the        target can be placed in the optical axis of the optical system,    -   a single step of exposure of the target is performed with the        optical system positioned so as to cooperate with the target,        whereby the three-dimensional relative position between the        holder of the workpiece to be machined and the tool-holder is        determined.

According to an embodiment of this method, in the exposure step, theoptical system and the target are positioned such that the image focalplane of the optical system can be merged with the useful face of thetarget.

According to this method, it is also possible to provide one or other orseveral of the following provisions:

-   -   said target is three-dimensional, and comprises, on a useful        face:        -   a first structure defining a planar reference face divided            up between at least:            -   a first portion whose surface is reflective according to                a diffuse reflection, and            -   a second portion whose surface is reflective according                to a specular reflection, and        -   a second structure having a face that is inclined relative            to said planar reference face,    -   said optical system comprises a first exposure system and a        second exposure system, in which:        -   the depth of field of the first exposure system is at least            10 times greater than the depth of field of the second            exposure system, and        -   said optical system is arranged on the one hand such that            the optical path of the first exposure system and the            optical path of the second exposure system have a common            section comprising the image focal plane of the first            exposure system and the image focal plane of the second            exposure system, and, on the other hand, such that the            difference between the focal distance of the second exposure            system and the focal distance of the first exposure system            lies between the minimum distance and the maximum distance            separating the reference face from the inclined face,    -   the tool-holder and the work-holder are positioned such that, on        the one hand, the focal distance of the first exposure system        can place the image focus of the first exposure system on the        first structure of the target and that, on the other hand, the        focal distance of the second exposure system can place the image        focus of the second exposure system on the second structure of        the target,    -   in said step of exposure with the optical system, at least one        exposure is taken simultaneously with the first exposure system        of the optical system and with the second exposure system of the        optical system, whereby, for each exposure by the optical        system, on the one hand, the first exposure system generates a        first image of the target making it possible to identify, on the        reference face, the position of the second portion relative to        the first portion, which gives, firstly, a first piece of        information on the relative position according to the direction        X of the target relative to the first exposure system and,        secondly, a second piece of information on the relative position        between the target and the first exposure system according to        the direction Y, and, on the other hand, the second exposure        system generates a second image of the target comprising a sharp        portion corresponding to a location of the inclined face of the        second structure, which gives a third piece of information on        the distance between said target and said second exposure system        according to the direction Z.

According to another possible provision, said second portion of theplanar reference face is divided up according to a series of localizedzones positioned in the first portion and in which, when said firstexposure system generates a first image of the target, the position ofthe localized zones of the second portion is identified on the referenceface, which gives a piece of information on the relative positionbetween said localized zones and the first exposure system making itpossible to deduce the relative measurement according to the direction Yand according to the direction X.

BRIEF DESCRIPTION OF THE FIGURES

Examples of implementation of the invention are indicated in thedescription illustrated by the attached figures in which:

FIG. 1 illustrates a three-dimensional measuring device comprising athree-dimensional target and an optical system,

FIG. 2A illustrates the use of the three-dimensional measuring device ofFIG. 1 in a machine-tool according to the invention for the measurementin space of the relative position between the tool-holder and thework-holder (also called material spindle),

FIG. 2B shows the part of FIG. 2A corresponding to the tool-holder withthe three-dimensional target, from the direction IIB of FIG. 2A, i.e.according to the direction Z, as seen by the optical system when thetarget is oriented towards the optical system,

FIGS. 3A, 3B and 3C are three views illustrating the structure of thethree-dimensional target, respectively from the front, in perspectiveand in cross section, and FIGS. 3D and 3E are perspective views of thesecond structure of the target respectively as in FIGS. 3A, 3B and 3Cand according to a variant embodiment,

FIGS. 4A and 4B illustrate the processing of the image generated by thesecond exposure system of the optical system,

FIG. 5 represents, in perspective and in an exploded view, a tool-holderequipped with the three-dimensional target,

FIG. 6 illustrates the mounting of the three-dimensional opticalmeasuring device in a tool-holder according to the invention.

EXEMPLARY EMBODIMENT(S) OF THE INVENTION

FIG. 1 shows an optical device 10 comprising an optical system 100 and athree-dimensional target 200 that can cooperate together to perform thethree-dimensional measurement of the relative position between thetarget 200 and the optical system 100. In fact, in this measurementposition, the target 200 is oriented towards the optical system 100,parallel to a main axis, forming a main horizontal direction Z. To thisend, at the output of the optical system 100, the optical path O isorthogonal to a useful face 202 of the target 200.

The target 200 is now described in relation to FIGS. 1, 3A, 3B and 3C.The target 200 takes the form of a pellet, here of cylindrical form ofcircular section (it could be of square or other section), of which oneside forms the useful face 202 for the performance of the measurement.For the performance of the measurement, this useful face 202 istherefore turned towards the optical system 100, and in particulartowards the input face 102 of the optical system 100, the axis Zcorresponding to the main direction (horizontal in the figures)separating the useful face 202 from the input face 102 of the opticalsystem 100.

The surface of the useful face 202 of the target 200 is divided upbetween a first structure 210 and a second structure 220. The firststructure 210 comprises a planar reference face 212 whose surface issmooth and is divided up between a first portion 214 whose surface isreflective according to a diffuse reflection and a second portion 216whose surface is reflective according to a specular reflection. In oneembodiment, the first portion 214 is coated with a diffusing reflectivelayer, for example of barium sulfate BaSO4, and the second portion 216is formed by a layer that is reflective according to a specularreflection, for example of chromium. In the embodiment illustrated, thesecond portion 216 is made up of several localized zones 217 in the formof circles forming islands positioned within the first portion 214 whichis continuous. These localized zones 217 can take other forms, such assegments or islands of a form other than a circle. These localized zones217 define, between them, a geometrical figure belonging to thefollowing list: quadrilateral, parallelogram, rectangle, square,rhombus, regular polygon and circle. This geometrical figure can be ageometrical figure with central symmetry. In FIGS. 3A and 3B, twentyfour circular localized zones 217 are arranged in a square. The aim ofthis first structure 210 is to be able to accurately identify the centreC3 thereof using standard vision tools. With the square form, the twodiagonals C1 and C2 of the square are secant at the centre of thesquare. It should be noted that, in the measurement position, asrepresented in FIGS. 1 to 3 and 5, the reference face 212 is positionedparallel to the directions X and Y, respectively forming a verticaldirection (axis) and a transverse horizontal direction (axis) in thecase of the arrangement illustrated.

The second structure 220 comprises a face which is inclined 222 relativeto the reference face 212: this inclined face 222 is essentially planar,the median plane of this inclined face forming, relative to thereference face 212, an acute angle α lying between 10 degrees and 80degrees, for example between 20 and 30 degrees, and preferably of theorder of 25 degrees (see FIG. 3C).

In one embodiment, the surface of this inclined face 222 is not smoothbut has relief elements 224 forming surface irregularities, which areeither random or else according to a predetermined geometry, for exampledefining between them a form of grid or a network of lines, thusconstituting a structured grid (not represented) or structured networkof lines (see FIG. 3D).

Such relief elements 224 can be protruding or hollowed out, that is tosay set back, relative to the median plane of the inclined face 222,particularly in the form of small roughnesses, or any other surfaceirregularity. Such relief elements 224 can be present over all thesurface of the inclined face 222. Such relief elements can be evenlydistributed over all the surface of the inclined face 222. For example,these relief elements 224 can form a set delimiting a grid or networkpattern, or more generally a structured surface or a rough surface whichmakes it possible to have the light reflected on this inclined face 222well diffused. The surface of the inclined face 222 of the secondstructure 222 is for example covered by one of the following elements:etched network or structured grid, with a pitch between the patterns ofthe grid or of the network lying between 5 and 100 micrometres, inparticular between 5 and 50 micrometres, and in particular between 8 and15 micrometres, for example of the order of 10 micrometres.

For example, this inclined face 222 is made of non-polished silicon orelse of ceramic, or of non-polished metal or of glass, or any otherstructurable material, and the relief elements 224 have been obtained byphotolithography, machining by chip removal, direct writing, etc., orany other structuring method. These relief elements 224 form, forexample, depressions and/or protuberances respectively set backfrom/extending beyond the median plane by a few micrometres or by a fewtens of micrometres, in particular between 0.5 and 50 micrometres.

In another embodiment, as illustrated in FIG. 3E, the surface of thisinclined face 222 is smooth and comprises a network of lines ofchromium, or of another material resulting in a specular reflection ofthese lines of chromium which constitute specular elements 225. Thesespecular elements 225 in the form of lines are positioned parallel toone another. In the measurement position, these specular elements 225 inthe form of lines or strips are positioned parallel to the plane Y, Z,such that, along the inclined surface, in the direction Z, these linesare encountered one by one (this is also the case when advancing in thedirection X). The substrate forming the wafer of the second structure220 can then be made of different materials, including glass or silicon,with, on the inclined face 222, a diffusing reflective layer, forexample made of barium sulfate BaSO₄ which alternates with the specularelements 225 or else which covers all the surface of the inclined face,with the specular elements 225 positioned above this diffusingreflective layer. In an exemplary embodiment, these specular elements225 in the form of lines form a network with a pitch of 25 micrometres,the lines (in particular of chromium) having a width of 12.5micrometres, equal to the width of the line spacing or portion with adiffuse reflection which is also in the form of a lines or strip 12.5micrometres wide. According to another implementation, a pitch of 10micrometres or, more generally, a pitch between 5 and 50 micrometres, isused. It should be noted that these specular elements 225 whichalternate with the rest of the surface which produces a diffusereflection, could take forms other than continuous lines or segmentsforming strips, in particular discontinuous lines or broken lines,patterns such as dotted borders, circles, triangles, or any othergeometrical form.

According to an embodiment that is not illustrated, the inclined face222 of the second structure 220 bears spot, protruding relief elements224, in the form of small mounds or spikes, which are distributed inmutually parallel rows, the relief elements 224 being mutually offsetfrom one row to another, to form a staggered pattern. According toanother embodiment that is not illustrated, the inclined face 222 of thesecond structure 220 bears protruding relief elements 224 in the form ofsegments that are parallel to one another and equidistant according totwo series intersecting at 90° to one another. This set of reliefelements 224 constitutes a grid pattern. It should be noted that thisgrid can be formed by two series of mutually parallel segments, withseries of segments intersecting according to an angle other than 90° toone another. In FIGS. 3A, 3B, 3C and 3D, the inclined face 222 of thesecond structure 220 bears relief elements 224 hollowed out in the formof a series of segments that are parallel to one another and equidistantfrom one another along the direction X: these relief elements 224 form,in this case, grooves. This direction X is therefore orthogonal to thedirection of the segments forming the relief elements 224.

In the embodiment of FIG. 3E, the surface of the inclined face 222 ofthe second structure 220 is therefore covered by a network of specularlines 225, namely of mutually parallel continuous strips whose surfacehas specular reflection properties.

Thus, in some of the abovementioned cases, and in particular those ofFIGS. 3D and 3E, the surface of the inclined face 222 of the secondstructure 220 is striated.

According to the embodiments represented for the target 200, the pelletdelimiting the target 200 comprises, on its useful face 202, the firststructure 210 which occupies most of the surface of the useful face 202,and, within the first structure 210, a zone reserved for the secondstructure 220. In this situation, the first structure 210 surrounds thesecond structure 220. More specifically, the localized zones 217 of thesecond portion 216 of the first structure 210 define a square whichsurrounds the second structure 220. According to one possible provision,and in the case of the embodiments of the target 200 as represented, thefirst structure 210 and the second structure 220 are positioned on theuseful face 202 concentrically to one another. Moreover, as in the casesrepresented, the first structure 210 delimits an aperture 218 for ahousing 219 housing said second structure 220, which is for examplepositioned on a wafer having the inclined face 222. When the wafer ishoused in the housing 219 of the first structure 210, its inclined face222 is turned towards the outside of the housing 219, towards theaperture 218. In this particular case, the second structure 220 ispositioned in said housing 219 with the inclined face 222 which is setback relative to the reference face of said first structure 210: thismeans that the inclined face 22, therefore the second structure 220, ispositioned to the rear, behind the plane delimited by the reference face212 (relative to the main direction Z, see FIG. 3B), in the housing 219,and is so set back for example by 0.05 to 2 millimetres or else byaround 0.15 millimetres. According to another possibility, notrepresented, the second structure 220 is positioned to the fore, infront of the plane delimited by the reference face 212. According to yetanother possibility, not represented, the second structure 220 ispositioned on either side of the plane delimited by the reference face212, namely a part of the inclined face 222 is positioned behind and theother part of the inclined face 222 is positioned in front, relative tothe reference face 212.

In order to protect the first structure 210 and the second structure 220from the environment (dust, oil, impacts, etc.), as can be seen in FIG.3C, the target 200 comprises a protection plate 230 in a transparentmaterial, in particular glass, covering the first structure 210 and thesecond structure 220 on the side of the useful face 202. According toone implementation possibility, as represented in FIG. 3C, the target200 comprises, in the form of a stack, the following elements. A bottomwall 231 is topped by a top plate 232 formed by a plate cut out at itscentre in order to delimit the housing 219 delimited by the aperture 218on the side of the useful face 202. The top plate 232 is topped by theprotection plate 230 closing the housing 219. The whole is surrounded bya cylindrical wall 234 retaining all of the target 200. The secondstructure 220 is for example a wafer of silicon housed in the housing219 with the inclined face 222 (bearing the relief elements 224 orspecular elements 225) turned towards the useful face 202. The face ofthe top plate 232 turned towards the useful face 202 comprises areflective layer 233 in two zones as described previously respectivelyin relation to the first portion 214 (reflective surface according to adiffuse reflection) and the second portion 216 (reflective surfaceaccording to a specular reflection, in particular in the form oflocalized elements 217).

Moreover, the target 200 can be equipped with a chip of RFID (radiofrequency identification) type, not represented, in order to allow thestorage and reading of a unique identifier and of data related to thetarget 200 and related to a first object on which the target 200 isintended to be mounted, in particular a tool-holder 310 (see FIGS. 5 and6): for example, the reference of this tool-holder 310 and otherinformation linked to the use of this tool-holder (for example itsserial number, its type, its setting relative to the material centre orwork-holder, the number of times it has been used, etc.).

Reference is now made to FIG. 1 to present the optical system 100associated with the target 200 which has just been described to form,together, an optical device 10 allowing the measurement of the relativeposition between two objects according to the three directions of space.In particular, an orthonormal space is considered in a Cartesianreference frame X, Y and Z, which is direct in the figures. This opticalsystem 100 is intended to simultaneously take, in the same sequence ofexposures, both an image of the first structure 210 of the target 200and at the same time an image of the second structure 220 of the target200. According to the present text, this simultaneous exposure of thetwo images is performed without adjustment, which allows for greatrapidity of execution of this exposure. Other features, linked inparticular to the specific structure of the target 200 which has justbeen described, also allow a maximal accuracy. The applicant company hasproduced a three-dimensional optical measuring device 10 according tothe present description that has managed to produce, in a half-second orless, a repeatable relative measurement with an accuracy of onemicrometre or less.

This optical system 100 comprises a first exposure system 110 and asecond exposure system 120. According to one provision, said opticalsystem 100 is arranged such that the difference between the focaldistance of the second exposure system 120 and the focal distance of thefirst exposure system 110 lies between the minimum distance and themaximum distance separating the reference face 212 from the inclinedface 202. According to another provision, the depth of field DOF1 of thefirst exposure system 110 is much greater and in particular at least tentimes greater than the depth of field DOF2 of the second exposure system120. For example the depth of field DOF1 of the first exposure system110 is between 10 and 10,000, or even between 100 and 5000 times greaterthan the depth of field DOF2 of the second exposure system 120. Amongdifferent possibilities, the depth of field DOF1 of the first exposuresystem 110 is greater than or equal to 0.8 millimetres, or else it liesbetween 0.5 and 5 millimetres, or else it lies between 0.8 and 3millimetres, or else it lies between 1 and 2 millimetres. Also,according to different possibilities, the depth of field DOF2 of thesecond exposure system 120 is less than or equal to 0.1 millimetres, orelse it lies between 5 and 50 micrometres, or else it lies between 8 and30 micrometres, or else it lies between 10 and 20 micrometres.

This allows the first exposure system 110 to naturally and without othersetting, focus on all the reference face 212 of the first structure 210within a range of distance between the target 200 and the first exposuresystem 110 that can vary over a few millimetres. In parallel, the secondexposure system 120 is capable of naturally and without other settingfocusing on the portion of the inclined face 222 of the second structure210 which is at a distance from the second exposure system 120corresponding to the focal distance of the second exposure system 120.According to one possibility, the enlargement of the first exposuresystem 210 is less than the enlargement of the second exposure system220.

Each exposure system within the meaning of the present text (firstexposure system 210 and second exposure system 220) corresponds to anoptical system, in particular a centred optical system, comprising a setof optical components and an image acquisition system. Such an imageacquisition system makes it possible to take photographs and/or videos,and is for example a camera or a photographic appliance, in particular adigital photographic appliance. According to one possible provision, thefirst image acquisition system 112 of the first exposure system 110 andthe second image acquisition system 122 of the second exposure system120 are synchronized in order to simultaneously take a first image bythe first exposure system 110 and a second image by the second exposuresystem 120.

To allow the simultaneous access to the vision of the target 200 by thefirst exposure system 210 and by the second exposure system 220, thelatter have a common portion of optical path which is directed towardsand originates from the object watched by the optical system 100, inthis case the target 200 (see FIGS. 1 and 2) after the target 200 ismounted on the first object and the optical system 100 is mounted on thesecond object. To this end, in the measurement position, the firstexposure system 210 is turned towards the useful face 202 of the target200 and forms an exposure system aligned with the target 200, and thesecond exposure system 120 has an optical path 126 which meets theoptical path 116 of the exposure system 110 aligned with the target 200and forms an exposure system that is off centre relative to the target200, relative to the optical axis O of the optical system 100, andrelative to the common portion of the optical paths 116 and 126 (alignedwith the target). In other words, the optical path of the exposuresystem aligned with the target 200 is substantially at right angles tothe reference face 212. The optical axis O is superimposed with themedian ray of the common portion of the first optical path 116 and ofthe second optical path 126. In this common portion, the sections of thefirst optical path 116 and of the second optical path 126 are mutuallyparallel, but not necessarily superimposed.

In particular, as illustrated in FIGS. 1 and 2, the first exposuresystem 210 is turned towards the useful face 202 of the target 200, inother words is oriented at right angles to the useful face 202 of thetarget 200. This means that the optical axis O and the common portion ofthe optical paths 116 and 126 are aligned with the target 200 and are atright angles to the useful face 202 (and therefore to the reference face212) of the target 200. In this configuration, as is seen in FIGS. 1 and2, the optical axis O and the common portion of the optical paths 116and 126 are parallel to the main direction Z, and are orthogonal to thetransverse directions X and Y, and to the plane X, Y.

In the common portion of the optical paths 116 and 126, the optical raysare at least partly merged with or else simply parallel to one another.The second exposure system 120 which is off centre has a portion ofoptical path 126 internal to this second exposure system 120 which ispreferably parallel to the optical axis O. This internal portion ofoptical path 126 is linked to, or more specifically meets, the opticalpath 116 of the first exposure system 110 aligned by a dedicated opticalmodule 128, comprising a catoptric optical system such as a mirror 129.In this way, the input of the off-centre exposure system (here thesecond exposure system 120) is linked to the trajectory or optical pathof the aligned exposure system (here the first exposure system 110).

More generally, it is understood that one out of the first exposuresystem 110 and the second exposure system 120 is turned towards theuseful face 202 of the target 200 and forms an exposure system alignedwith the target 200, and the other exposure system out of the firstexposure system 110 and the second exposure system 120 has an opticalpath 126 which meets the optical path 116 of the exposure system 110aligned with the target 200 and forms an off-centre exposure system.This means that the other exposure system has an optical axis whichpasses through the inclined face 222, that is to say the secondstructure 220 of the target 200. Also, the first exposure system 110 andthe second exposure system 120 are positioned in parallel to oneanother. Furthermore, the optical system also comprises an opticalmodule 128 (for example with a catoptric optical system such as amirror) positioned between the first exposure system 110 and the secondexposure system 120 and configured to deflect a portion of the lightrays passing through at least a part of one out of the first and thesecond exposure systems to the other of the first and the secondexposure systems. Conversely, the optical system 100 is arranged suchthat the optical path from the object watched (the target 200 in FIGS. 1and 2) by the optical system 100 passes through at least a portion ofone out of the first exposure system 110 and the second exposure system120 (the first exposure system 110 in FIGS. 1 and 2) before reaching theother out of the first exposure system 110 and the second exposuresystem 120 (the second exposure system 120 in FIGS. 1 and 2).

In one embodiment, the focal distance of the second exposure system 120is greater than the focal distance of the first exposure system 110. Forexample, the difference between the focal distance of the secondexposure system 120 and the focal distance of the first exposure system110 lies between 0.5 and 5 millimetres.

In one embodiment, the enlargement of the first exposure system 110 isless than or equal to the enlargement of the second exposure system 120.For example, the enlargement of the first exposure system 110 liesbetween 0.2 and 1 times the enlargement of the second exposure system120. For example, the enlargement of the first exposure system 110 liesbetween 0.3 and 0.8, or else between 0.4 and 0.6, preferably around 0.5times the enlargement of the second exposure system 120.

In the embodiment of FIGS. 1 and 2, the optical system 100 alsocomprises a light source 140 oriented towards the three-dimensionaltarget 200, this light source 140 being positioned in order toconstitute a lateral illumination of the three-dimensional target 200.To this end, this light source 140 is arranged off centre and inclinedrelative to the optical path 116+126 of the optical system 100. Inparticular, the light rays from the light source 140 form, with thereference face 212 of the target, an angle such that their specularreflection on the reflective surfaces of the target, and in particularon the localized zones 217, generates reflected light rays which do notenter into the optical system 100. Likewise, when the inclined face 222comprises specular elements 225, the reflection of the light rays fromthe light source 140 on these specular elements 225 does not enter intothe optical system 100.

According to one embodiment, the first exposure system 210 used and thesecond exposure system 220 used are telecentric. As a reminder,telecentricity is a characteristic of an optical system in which all themain rays (the central ray of each beam of rays) which pass through thesystem are practically collimated and parallel to the optical axis. Inthe case of telecentric optics, the notion of depth of field is replacedby that of working distance. According to another embodiment, the firstexposure system 210 used and the second exposure system 220 used arenot, or are not both, telecentric. In the case where they are bothtelecentric, they can be used also to measure the geometricalcharacteristics of the tools positioned on the tool-holder 310.

Reference is now made to FIGS. 2A and 6 to explain the method forthree-dimensional optical measurement between the target 200 and theoptical system 100, in the case of a machine-tool whose machining module300 comprises such an optical device 10. The reference directions X, Yand Z taken are those of the machine-tool, in particular of the frame ofthe machine-tool, which gives a vertical direction X (or firsttransverse axis), a main horizontal direction Z (or main axis) and alateral horizontal direction Y (or second transverse axis). The target200 is placed on the tool-holder 310 serving as first object (see FIG.5): the tool-holder 310 extends in a horizontal main direction,corresponding to the axis X, with the possibility of rotating about thisaxis X. To this end, a part of the tool-holder 310, for example theclamp, has recesses on its periphery, usually dedicated to the mountingof the clamp gripping/releasing tool, in which the target 200 can beplaced, possibly associated with an RFID chip as explained previously.Moreover, the optical system 100 is mounted on the work-holder 320serving as second object (see FIG. 6) and receiving the workpiece to bemachined 322. The work-holder 320 extends along its horizontal maindirection, corresponding to the axis Z, with the possibility of rotatingabout this axis Z. Then, the work-holder 320 and the tool-holder 310 areplaced in a close position, prior to a machining step, placing the tool312 and the workpiece to be machined in proximity to one another, in arelative measurement position. The positioning of the target 200 on thetool-holder 310 and the positioning of the optical system 100 on thework-holder 320 make it possible, in this relative measurement position,to place the target 200, and more specifically the reference face 202,in the extension of the optical axis O of the optical system 100 (notethat this optical axis O is parallel to the direction Z). Thus, thereference face 202 of the target 200 is turned towards the input face102 of the optical system 100.

As in the case represented in FIG. 6, the optical device 10 alsocomprises a third exposure system 130 positioned on the tool-holder 310and configured to register the orientation of the useful face 202 of thetarget 200 and/or the angular orientation of the rotary part of thetool-holder 310, in particular about the axis X. A preliminaryadditional step, of positioning of the target 200, is performed beforethe step of simultaneous exposure with said optical system 100,according to which:

-   -   the tool-holder 310 and the work-holder 320 are positioned such        that the useful face 202 of the three-dimensional target 200 is        in the optical path O of the optical system 100. In particular,        the third exposure system 130 can be used to register the        angular orientation of the target 200 relative to the rotary        part of the tool-holder 310, therefore relative to the axis X,        which makes it possible to modify, if necessary, the angular        orientation of the rotary part of the tool-holder 310 (see the        arrow R in FIG. 6), and thus place the target 200 such that its        useful face 202 is turned towards the optical system 100. The        relative measurement position is obtained in which, when the        target 200 is oriented towards the optical system 100 as        explained previously in the case of FIGS. 1 and 2A, is obtained:        in this case, the direction Z extends between the target 200 and        the optical system 100.

In the first use of the optical device 10, namely of the optical system100 and of an associated target 200, respectively mounted on awork-holder 320 (or more generally a second object) and on a tool-holder310 (or more generally a first object), a preliminary additional stephas to be performed, of spatial referencing of the position of thetarget 200 relative to the tool-holder 310 (or more generally a firstobject) which bears the target 200 in the three directions X, Y and Z.It should be noted that, obviously, the parameters of the optical system100, namely of the first exposure system 110 and of the second exposuresystem, are known, including their focal distance. At this stage, it canbe mentioned that when the work space of the machining module 300 isconfined and maintained at constant temperature, this thermal stabilitygenerates a dimensional stability in the optical device 10 and thereforein its parameters.

It is recalled that the measurement of the three-dimensional relativeposition between the target 200 and the optical system 100 is used inthe case of a machine-tool to ultimately know the three-dimensionalrelative position in terms of X, Y and Z between the tool-holder 310 (ormore generally a first object) and the work-holder 320 (or moregenerally a second object).

In the present text, the three directions X, Y and Z are, for example,the axes of the machining module 300 of the machine-tool. Thus, Z can bedefined as being the main axis, namely the main horizontal directionseparating the first object (the tool-holder 310) from the second object(from the work-holder 320). X can be defined as the vertical directionor, more generally, a first transverse axis, and Y can be defined as alateral horizontal direction or, more generally, a second transverseaxis. In one embodiment, the tool-holder 310 rotates about an axisparallel to this direction X.

In this step of spatial referencing of the position in the threedirections X, Y and Z of the target 200 (calibration of the opticaldevice 10), for example with the arrangement of FIGS. 2A and 2B, anexposure by the optical system 100 is activated which results, on theone hand, in the generation by the first image acquisition system 112 ofthe first exposure system 110 of a first image of all the useful face202 of the target 200 with all the reference face 212 which is sharpand, on the other hand, the generation by the second image acquisitionsystem 122 of the second exposure system 120 of a second image of allthe inclined face 222 of the target 200 with only a sharp zone in theform of a horizontal strip. This first image comprises the image of thelocalized zones 217, here delimiting a square (see FIG. 3A), such thatthe processing of the first image generates the diagonals C1 and C2 ofthe square and makes it possible to identify the centre C3 of thesquare. Thus, since the position of the optical axis O on the firstimage is known, the determination of the position of the centre C3 ofthe square makes it possible to know the position in terms of X and interms of Y of the target 200 relative to the optical axis O, but also,on the one hand, relative to a reference point 314 in the direction X onthe tool-holder 310 and, on the other hand, relative to a referencepoint 316 in the direction Y on the tool-holder 310. In effect, as canbe seen in FIGS. 2A and 2B, as X reference, a face of the tool-holder310 is used which is orthogonal to the axis X, for example resultingfrom a recessed shoulder along a section of the tool-holder 310, visibleas a line on the first image and which face forms said reference point314 in the direction X. Furthermore, as can be seen in FIGS. 2A and 2B,as Y reference, a dimension of the tool-holder 310 in proximity to thetarget 200 is used, which is orthogonal to the axis X, and in the caserepresented which is the width (parallel to the direction Y) of thetool-holder 310 in proximity to the target 200, for example the diameterwhen this portion of the tool-holder 310 is cylindrical of circularsection; this dimension forms said reference point 316 in the directionY.

In parallel, the processing of the second image, an example of which isvisible in FIG. 4A, is performed. Through the analysis of the localcontrast of this second image (see FIG. 4B representing curves ofcontrast as a function of the position in terms of X), the position X0in the vertical direction X of the sharp zone of the second image isdetermined. This analysis is done via an algorithm that makes itpossible to determine the sharpest pixels of the image. Since theinclination of the inclined face 222 is known, a curve is obtained ofmapping between X and Z of this inclined face 222, specific to thetarget 200. By virtue of this mapping curve, the knowledge of theposition X0 (see FIGS. 4A and 4B) makes it possible to deduce therefromthe position Z0 of the inclined face 222 on the optical axis O, andtherefore the position in terms of Z of the target 200 relative to theoptical system 100. Moreover, the relative position in terms of Z of theoptical system 100 relative to the work-holder 320 is known through ameasurement rule (not represented) positioned along the axis X on thework-holder 320 and which supports the optical system 100. Similarly,the relative position in terms of Z of the target 200 relative to thereference point 314 of the tool-holder 310 is known.

By performing this operation multiple times, each time modifying thedistance in terms of Z of the work-holder 310 relative to thetool-holder 320 (for example by retracting or advancing the work-holder310), it is thus possible to reconstruct the three-dimensional image ofthe inclined face 222 of the target 200, and have a reference baseforming a mapping for the three-dimensional coordinates of the inclinedface 222 of the target 200 relative to the tool-holder 310. Ultimately,it is all of the useful face 202 of the target 200 (reference face 212and inclined face 222) which is spatially referenced in the threedirections X, Y and Z relative to the tool-holder 310.

Next, the actual measurement can be performed whenever necessary duringoperations of use of the machining module 300 equipped with this target200 and with this optical system 100, not dismantled betweentimes toconserve the accuracy of the measurement of the spatial referencingexplained previously. To this end, there is used for example thearrangement of FIG. 2A. If necessary, a rotation of the work-holder 320is performed about its axis of rotation which is parallel to the axis X(see the arrow R in FIG. 6), to align the target 200 with the opticalsystem 100. Then, an exposure by the optical system 100 is activated,which results, on the one hand, in the generation by the first imageacquisition system 112 of the first exposure system 110 of a first imageof all the useful face 202 of the target 200 with all the reference face212 which is sharp and, on the other hand, the generation by the secondimage acquisition system 122 of the second exposure system 120 of asecond image of all the inclined face 222 of the target 200 with only asharp zone in the form of a horizontal strip corresponding to the focaldistance of the second exposure system 120. The analysis of this firstimage makes it possible, as explained previously, to identify the centreC3 of the square formed by the localized elements 217, and thus theposition in terms of X and in terms of Y of the target 200 relative tothe optical axis O, and also relative to the tool-holder 310. Theanalysis of the second image and in particular of the position of thesharp zone of the second image (as in FIG. 2A) in the direction X makesit possible to know the position in terms of Z, therefore the distance,of the target 200 relative to the optical system 100. In effect, for thesecond image, since the position Z of each pixel of the image of theinclined face 222 relative to the references 314 and 316 on thetool-holder 310 is known, it is possible to very rapidly measure theposition Z of the target 200 and therefore of the tool-holder 310.

It will be understood from the above that, in this way, solely throughthe analysis of the two images generated by the optical system 100,without a loss of time that a setting or an adjustment of this opticalsystem 100 would entail, the position in terms of X, Y and Z of thetarget 200 relative to the optical system 100 and starting from thetool-holder 310 relative to the work-holder 320, is very rapidlymeasured. This is possible because the position in terms of X, Y and Zof the optical system 100 relative to the work-holder 320 is known.

The present text relates also to an optical system for thethree-dimensional measurement of the relative position between a firstobject and a second object on which said optical system is intended tobe mounted, said optical system comprising a first exposure system and asecond exposure system, in which:

-   -   the depth of field of the first exposure system is at least 10        times greater than the depth of field of the second exposure        system,        and    -   the optical system is arranged such that the optical path of the        first exposure system and the optical path of the second        exposure system have a common section comprising the image focal        plane of the first exposure system and the image focal plane of        the second exposure system.

The present text relates also to a method for three-dimensional opticalmeasurement according to three orthogonal directions X, Y and Z, betweena first object and a second object that are aligned and remote from oneanother in the main direction Z, in which:

-   -   a three-dimensional target is provided comprising, on a useful        face forming a positioning reference:        -   a first structure defining a planar reference face divided            up between at least:            -   a first portion whose surface is reflective according to                first reflection parameters, and            -   a second portion whose surface is reflective according                to second reflection parameters different from the first                reflection parameters, and        -   a second structure having a face that is inclined relative            to said planar reference face    -   an optical system is provided        comprising a first exposure system and a second exposure system,        in which:    -   the depth of field of the first exposure system is at least 10        times greater than the depth of field of the second exposure        system, and    -   said optical system is arranged, on the one hand, such that the        optical path of the first exposure system and the optical path        of the second exposure system have a common section comprising        the image focal plane of the first exposure system and the image        focal plane of the second exposure system,        and, on the other hand, such that the difference between the        focal distance of the second exposure system and the focal        distance of the first exposure system lies between the minimum        distance and the maximum distance separating the reference face        from the inclined face,    -   said three-dimensional target is positioned on the first object        such that, on the one hand, the focal distance of the first        exposure system can place the image focus of the first exposure        system on the first structure of the target and, on the other        hand, the focal distance of the second exposure system can place        the image focus of the second exposure system on the second        structure of the target,    -   said optical system is positioned on the second object,    -   at least one exposure is performed simultaneously with the first        exposure system of the optical system and with the second        exposure system of the optical system,        whereby, for each exposure by the optical system, on the one        hand, the first exposure system generates a first image of the        target that makes it possible to identify, on the reference        face, the position of the second portion relative to the first        portion, which gives, firstly, a first piece of information on        the relative position according to the direction X of the target        relative to the first exposure system and, secondly, a second        piece of information on the relative position between the target        and the first exposure system according to the direction Y, and,        on the other hand, the second exposure system generates a second        image of the target comprising a sharp portion corresponding to        a location of the inclined face of the second structure, which        gives a third piece of information on the distance between said        target and said second exposure system according to the        direction Z.

As already explained previously, the optical system therefore generatesthe first image and the second image synchronously. Furthermore, theoptical system 100 generates the first image and the second imagewithout performing adjustment, which makes it possible to perform theexposure immediately and without loss of time.

The present text relates also to a machine-tool comprising an opticaltarget as defined previously, and a machine-tool comprising an opticalsystem as defined previously. The present text relates also to amachine-tool comprising a machining module equipped with a tool-holderand a work-holder, and an optical measuring device for thethree-dimensional measurement of the relative position between saidtool-holder and said work-holder, said optical measuring devicecomprising an optical system mounted on the work-holder and a targetmounted on the tool-holder and comprising a useful face forming apositioning reference that can be placed in the optical axis of theoptical system. For example, the optical measuring device is configuredto make it possible, through a single step of exposure of the target bythe optical system, to determine the three-dimensional relative positionbetween the holder of the workpiece to be machined and the tool-holder.Also, according to one possible provision, the target is positioned suchthat the image focal plane of the optical system can be merged with theuseful face of the target.

The present text also relates to an arrangement for thethree-dimensional optical measurement of the relative position between afirst object and a second object, comprising:

-   -   an installation comprising a first object and a second object,    -   an optical measuring device as described in the present text in        which;    -   the first exposure system is configured such that its image        focal plane is capable of corresponding to the reference face of        the first structure, and    -   the second exposure system is configured such that its image        focal plane is capable of being secant with the inclined face of        the three-dimensional target. According to a second possibility,        compatible with the above-mentioned first possibility or taken        alone, the optical measuring device is such that:    -   the focal distance of the first exposure system can make it        possible to place the image focus on the first structure,    -   the focal distance of the second exposure system can make it        possible to place the image focus on the second structure.

Such an installation is for example a piece of equipment, a machine, amodule, in particular scientific or technical, having a first object anda second object that can be moved relative to one another and for whichit is necessary to perform a referencing of relative position in thethree-dimensional space. For example, this installation is amachine-tool or a machining module with, as first object, thetool-holder or one of the tool-holders, and, as second object, thework-support bearing the piece to be machined (bar, blank, etc.).According to another example, this installation is a unit for mountingelectronic components on a PCB (printed circuit board), with, as firstobject, the support of the printed circuit board and, as second object,the clamp or other tool for mounting an electronic component. Accordingto yet another example this installation is a cell culture module forperforming the seeding of series of wells housed on microplates, thefirst object being the support of the microplate and the second objectbeing the support of the device for injecting the cells to becultivated.

The present text relates also to a method for three-dimensional opticalmeasurement in three orthogonal directions X, Y and Z, between a firstobject and a second object that are aligned and remote from one anotherin the main direction Z, in which:

-   -   a three-dimensional target is provided that includes, on a        useful face forming a positioning reference, and comprising:    -   a first structure defining a planar reference face divided up        between at least:    -   a first portion whose surface is reflective according to first        reflection parameters, and    -   a second portion whose surface is reflective according to second        reflection parameters that are different from the first        reflection parameters, and    -   a second structure having an inclined face relative to said        planar reference face    -   an optical system is provided comprising a first exposure system        and a second exposure system, in which:    -   said three-dimensional target is positioned on the first object        such that, on the one hand, the focal distance of the first        exposure system is capable of placing the image focus of the        first exposure system on the first structure of the target and,        on the other hand, the focal distance of the second exposure        system is capable of placing the image focus of the second        exposure system on the second structure of the target,    -   said optical system is positioned on the second object,    -   at least one exposure is taken simultaneously with the first        exposure system of the optical system and with the second        exposure system of the optical system, whereby, for each        exposure by the optical system, on the one hand the first        exposure system generates a first image of the target making it        possible to identify, on the reference face, the position of the        second portion relative to the first portion (in particular, the        position of the localised zones on the reference face), which        gives, firstly, a first piece of information on the relative        position in the direction X of the target relative to the first        exposure system and, secondly, a second piece of information on        the relative position between the target and the first exposure        system in the direction Y, and, on the other hand, the second        exposure system generates a second image of the target        comprising a sharp portion corresponding to a location of the        inclined face of the second structure, which gives a third piece        of information on the distance between said target and said        second exposure system in the direction Z. To this end,        according to one possibility, the depth of field (DOF1) of the        first exposure system is at least 10 times greater than the        depth of field (DOF2) of the second exposure system. Moreover,        according to another possibility, taken on its own or in        combination with the preceding one, said optical system is        arranged such that the optical path of the first exposure system        and the optical path of the second exposure system have a common        section including the image focal plane of the first exposure        system and the image focal plane of the second exposure system.        Moreover, according to another possibility, taken on its own or        in combination with the preceding possibility or both preceding        possibilities, the difference between the focal distance of the        second exposure system and the focal distance of the first        exposure system lies between the minimum distance and the        maximum distance separating the reference face from the inclined        face.

By this method, it is possible to have spatial geometrical informationlinked to the (first) reference face and to the inclined face or secondreference face of the three-dimensional target, making it possible todeduce therefrom the relative position in the three spatial directionsX, Y and Z between the first object and the second object. Previously,the referencing of the relative three-dimensional position between thetarget and the first object and the referencing of the relativethree-dimensional position between the optical system and the secondobject will have been performed.

It is essential to note that, in one embodiment, the exposure or imagegeneration by each exposure system of the optical system is performedwithout adjustment of the corresponding exposure system. Indeed, it isthe relative position in the three directions X, Y and Z of the exposuresystem relative to the object that it is looking at (and therefore boththe relative position of the first exposure system relative to thereference face of the target and the relative position of the secondexposure system relative to the inclined face of the target) and theoptical properties, and for example the very different depth of field ofeach exposure system of the optical system, which makes it possible tosimultaneously generate two images, respectively of the reference faceand of the inclined face. The analysis of these two images (even of twoseries of images) makes it possible to deduce therefrom information onthe relative position in terms of X (this direction X corresponding forexample to the height) and in terms of Y (this direction Y correspondingfor example to the horizontal lateral offset) and in terms of Z (thisdirection Z corresponding for example to the main horizontal distance)between the target and the optical system, and thus the relativethree-dimensional position between the first object which bears thethree-dimensional target and the second object which bears the opticalsystem.

In one embodiment, after the positioning of the three-dimensional targeton the first object and the positioning of the optical system on thesecond object, an additional step is performed, of spatial referencingof the position in terms of X, Y and Z of the target relative to thefirst object by the optical system.

According to one possible provision, the second portion of the planarreference face is divided up according to a series of localised zonespositioned in the first portion and the first image generated by thefirst exposure system makes it possible to identify the position of thelocalised zones of the second portion on the reference face, which givesa piece of information on the relative positon between said localisedzones and the first exposure system making it possible to deduce therelative measurement according to the direction Y and according to thedirection X.

REFERENCE NUMBERS USED IN THE FIGURES

X Vertical direction (first transverse axis)

Y Lateral horizontal direction (second transverse axis)

Z Main horizontal direction separating the first object from the secondobject (main axis)

C1 Diagonal

C2 Diagonal

C3 Centre

α Angle of the inclined face

R Arrow for the rotation of the tool-holder and of the target

10 Optical device

200 Three-dimensional target

202 Useful face

210 First structure

212 Reference face

214 First portion (reflective surface according to a diffuse reflection)

216 Second portion (reflective surface according to a specularreflection)

217 Localized zones

218 Aperture

219 Housing

220 Second structure

222 Inclined face

224 Relief elements

225 Specular elements

230 Transparent protection plate

231 Bottom wall

232 Top plate

233 Reflective layer

234 Cylindrical wall

100 Optical system

O Optical axis

102 Input face of the optical system

110 First exposure system

DOF1 Depth of field of the first exposure system

F1 Image focal plane of the first exposure system

112 First image acquisition system

116 Optical path of the first exposure system

120 Second exposure system

F2 Image focal plane of the second exposure system

DOF2 Depth of field of the second exposure system

122 Second image acquisition system

126 Optical path of the second exposure system

128 Optical module with catoptric optical system

129 Mirror

130 Third exposure system

140 Light source (lateral illumination)

300 Machining module

310 Tool-holder (first object)

312 Tool

314 Registration in terms of X on the tool-holder

316 Registration in terms of Y on the tool-holder

320 Work-holder or material spindle (second object)

322 Workpiece to be machined (material)

What is claimed is:
 1. Machine-tool comprising a machining moduleequipped with a tool-holder and a work-holder, and an optical measuringdevice for the three-dimensional measurement of the relative positionbetween said tool-holder and said work-holder, said optical measuringdevice comprising an optical system with an image acquisition system,mounted on the work-holder and a target mounted on the tool-holder andcomprising a useful face forming a positioning reference that can beplaced in the optical axis (O) of the optical system, wherein saidoptical measuring device is configured to make it possible, through asingle step of exposure of the target by the optical system to determinethe three-dimensional relative position between the holder of theworkpiece to be machined and the tool-holder.
 2. Machine-tool accordingto claim 1, wherein the target is positioned such that the image focalplane of the optical system can be merged with the useful face of thetarget.
 3. Machine-tool according to claim 1, wherein the target is athree-dimensional target comprising, on a useful face: a first structuredefining a planar reference face, and a second structure having a facethat is inclined relative to said planar reference face, and whereinsaid optical system comprises a first exposure system (110) and a secondexposure system, wherein the difference between the focal distance ofthe second exposure system and the focal distance of the first exposuresystem lies between the minimum distance and the maximum distanceseparating the reference face from the inclined face.
 4. Machine-toolaccording to claim 3, wherein said planar reference face is divided upbetween at least: a first portion whose surface is reflective accordingto first reflection parameters, and a second portion whose surface isreflective according to second reflection parameters different from thefirst reflection parameters.
 5. Machine-tool according to claim 4,wherein the surface of said first portion is reflective according to adiffuse reflection, and the surface of said second portion is reflectiveaccording to a specular reflection.
 6. Machine-tool according to claim4, wherein said second portion is divided up according to a series oflocalized zones positioned in the first portion.
 7. Machine-toolaccording to claim 3, wherein the surface of said inclined face hasrelief elements or else specular elements that are evenly distributed.8. Machine-tool according to claim 6, wherein said localized zonesdefine between them a geometrical figure belonging to at least one ofthe following: quadrilateral, parallelogram, rectangle, square, rhombus,regular polygon or circle.
 9. Machine-tool according to claim 6, whereinsaid localized zones of said second portion are formed by islands orsegments distributed in the first portion
 10. Machine-tool according toclaim 3, wherein the first structure and the second structure arepositioned on the useful face concentrically to one another. 11.Machine-tool according to claim 3, wherein the first structure surroundsthe second structure.
 12. Machine-tool according to claim 6, whereinsaid localized zones of the second portion of the first structure definea square which surrounds the second structure.
 13. Machine-toolaccording to claim 3, wherein the first structure delimits an aperturefor a housing housing said second structure.
 14. Machine-tool accordingto claim 13, wherein the second structure is positioned in said housingwith the inclined face which is set back relative to the reference faceof said first structure.
 15. Machine-tool according to claim 3, whereinthe surface of the inclined face of the second structure is striated, inparticular the surface of the inclined face of the second structure iscovered by one of the following elements: etched network, structuredgrid or network of specular lines.
 16. Machine-tool according to claim7, wherein said target also comprises a plate in a transparent material,in particular glass, covering the first structure and the secondstructure on the side of the useful face.
 17. Machine-tool according toclaim 3, wherein said optical measuring device also comprises a lightsource oriented towards the three-dimensional target, said light sourcebeing positioned in order to constitute a lateral illumination of thethree-dimensional target.
 18. Machine-tool according to claim 1, whereinthe optical system comprises a first exposure system and a secondexposure system, wherein: the depth of field of the first exposuresystem is at least 10 times greater than the depth of field of thesecond exposure system, and the optical system is arranged such that theoptical path of the first exposure system and the optical path of thesecond exposure system have a common section placed on the optical axis(O) of the optical system and comprising the image focal plane of thefirst exposure system and the image focal plane of the second exposuresystem.
 19. Machine-tool according to claim 18, wherein the opticalsystem is arranged such that the optical path from the object passesthrough at least a portion of one out of the first and the secondexposure systems before reaching the other of the first and the secondexposure systems.
 20. Machine-tool according to claim 18, wherein thefirst and the second exposure systems are positioned in parallel to oneanother and in that the optical system also comprises an optical modulepositioned between the first and the second exposure systems andconfigured to deflect some of the light rays passing through at least apart of one out of the first and the second exposure systems to theother out of the first and the second exposure systems.
 21. Machine-toolaccording to claim 18, wherein the focal distance of the second exposuresystem is greater than the focal distance of the first exposure system.22. Machine-tool according to claim 18, wherein the enlargement of thefirst exposure system is less than the enlargement of the secondexposure system.
 23. Machine-tool according to claim 18, wherein thedepth of field (DOF1) of the first exposure system is greater than orequal to 0.8 millimetres.
 24. Machine-tool according to claim 18,wherein the depth of field (DOF2) of the second exposure system is lessthan or equal to 0.1 millimetres.
 25. Machine-tool according to claim18, wherein the first exposure system is telecentric and the secondexposure system is telecentric.
 26. Machine-tool according to claim 3,wherein the optical system comprises a first exposure system and asecond exposure system, wherein: the depth of field of the firstexposure system is at least 10 times greater than the depth of field ofthe second exposure system, and the optical system is arranged such thatthe optical path of the first exposure system and the optical path ofthe second exposure system have a common section placed on the opticalaxis (O) of the optical system and comprising the image focal plane ofthe first exposure system and the image focal plane of the secondexposure system, and wherein: the first exposure system is configuredsuch that its image focal plane can correspond to the reference face ofthe first structure, and the second exposure system is configured suchthat its image focal plane can be secant with the inclined face of thethree-dimensional target.
 27. Machine-tool according to claim 18,wherein the optical device also comprises a third exposure systempositioned on the tool-holder and configured to register the orientationof the useful face of the target and/or the angular orientation of thetool-holder.
 28. Method for three-dimensional optical measurementaccording to three orthogonal directions X, Y and Z in thethree-dimensional space of a machine-tool, between a tool-holder and awork-holder that are aligned and remote from one another in the maindirection Z, wherein: an optical system is provided with an imageacquisition system, said optical system is mounted on the work-holder, atarget is provided comprising a useful face forming a positioningreference, said target is mounted on the tool-holder, the tool-holderand the work-holder are positioned such that the target can be placed inthe optical axis (O) of the optical system, a single step of exposure ofthe target is performed with the optical system positioned so as tocooperate with the target, whereby the three-dimensional relativeposition between the holder of the workpiece to be machined and thetool-holder is determined.
 29. Measurement method according to claim 28,wherein, in the exposure step, the optical system and the target arepositioned such that the image focal plane of the optical system can bemerged with the useful face of the target.
 30. Measurement methodaccording to claim 29, wherein: said target is three-dimensional, andcomprises, on a useful face: a first structure defining a planarreference face divided up between at least: a first portion whosesurface is reflective according to a diffuse reflection, and a secondportion whose surface is reflective according to a specular reflection,and a second structure having a face that is inclined relative to saidplanar reference face, said optical system comprises a first exposuresystem and a second exposure system, wherein: the depth of field of thefirst exposure system is at least 10 times greater than the depth offield of the second exposure system, and said optical system is arrangedon the one hand such that the optical path of the first exposure systemand the optical path of the second exposure system have a common sectioncomprising the image focal plane of the first exposure system and theimage focal plane of the second exposure system, and, on the other hand,such that the difference between the focal distance of the secondexposure system and the focal distance of the first exposure system liesbetween the minimum distance and the maximum distance separating thereference face from the inclined face, the tool-holder and thework-holder are positioned such that, on the one hand, the focaldistance of the first exposure system can place the image focus of thefirst exposure system on the first structure of the target and that, onthe other hand, the focal distance of the second exposure system canplace the image focus of the second exposure system on the secondstructure of the target, in said step of exposure with the opticalsystem, at least one exposure is taken simultaneously with the firstexposure system of the optical system and with the second exposuresystem of the optical system, whereby, for each exposure by the opticalsystem, on the one hand, the first exposure system generates a firstimage of the target making it possible to identify, on the referenceface, the position of the second portion relative to the first portion,which gives, firstly, a first piece of information on the relativeposition according to the direction X of the target relative to thefirst exposure system and, secondly, a second piece of information onthe relative position between the target and the first exposure systemaccording to the direction Y, and, on the other hand, the secondexposure system generates a second image of the target comprising asharp portion corresponding to a location of the inclined face of thesecond structure, which gives a third piece of information on thedistance between said target and said second exposure system accordingto the direction Z.
 31. Measurement method according to claim 30,wherein said second portion of the planar reference face is divided upaccording to a series of localized zones positioned in the first portionand wherein, when said first exposure system generates a first image ofthe target, the position of the localized zones of the second portion isidentified on the reference face, which gives a piece of information onthe relative position between said localized zones and the firstexposure system making it possible to deduce the relative measurementaccording to the direction Y and according to the direction X.